This invention relates to a process and apparatus that controls and monitors the power delivered to a tool without the use of a torque transducer. By monitoring the amount of power being delivered to the tool, a control is able to calculate the amount of torque the tool is generating.
Preciseness and consistency of torque are very important to mass production operations, such as automobile assembly plants. Power tool applied torque to threaded fasteners must be consistent. Industry typically incorporates the torque measuring or controlling device into the power tool. This is costly as torque transducers are very expensive. Also, this approach often has been unsatisfactory because the measurement is not direct enough. These attempts often lead to large, bulky tools.
For example, in a typical power tool, an input shaft applies torque to a spindle through a series of bevel gears on the shaft and spindle. A transducer measures the torque on the spindle through a torsionally resilient device strain gauges, a gear case, planet gears and ring gears. This circuitous path at best provides a slow response to peak torque values. Measuring torque without a transducer would provide a huge cost savings.
This torque system includes a controller, microprocessor, variable frequency drive (VFD) and a power tool. The control is the heart of the system. It is responsible for communicating with the VFD, tool, keypad and display. As the user operates the switches on the tool, the control dictates the frequency at which the VFD will run the tool. While the tool is running, the control also monitors the amount of current that the VFD is providing the tool. For every frequency that the VFD uses to stimulate the tool, a corresponding current to torque curve exists in the control""s non-volatile memory. The microprocessor through the control is able to use these current versus torque curves to select the optimal tool frequency and ultimately turn the tool off when the fastener it is driving has reached torque.